As a result of problems associated with organic solvents constituting in coating materials, such as the combustibility thereof, atmospheric pollution, worker safety, and sanitation problems, it has been hoped a rapid shift from organic-solvent-based coating materials to water-based coating materials.
On the other hand, in the field of automobiles, steel household items, and household electrical appliances, the use of pre-coated metal materials has been increasing in order to improve productivity.
Accordingly, in the field of surface preparation and coating, as well, in order to respond to such demands, various coating material compositions for use in pre-coated metal materials have been developed; however, in this field, as well, the shift from conventional organic-solvent-based coating materials to water-based coating materials is strongly desired.
Furthermore, in systems employing conventional organic-solvent-based coating materials, in order to obtain the conductivity which is a necessary condition for conducting an electro-deposition coating, the inventions disclosed in, for example, Japanese Patent Application, Second Publication, No. Sho 45-2430 and Japanese Patent Application, Second Publication, No. Hei 4-6882, disclose zinc-rich coating materials. Such zinc-rich coating materials are capable of electro-deposition coating; however, the smoothness of the coated surface is insufficient. Furthermore, in such zinc-rich coating materials, the coating film is unstable with respect to rust produced in the case in which corrosion occurs, and it is impossible to guarantee corrosion resistance over a long period of time (resistance to rust cannot be guaranteed), and moreover, after working, the coating film is easily fractured, and thus the resistance to corrosion after working is poor.
On the other hand, the inventions disclosed in Japanese Patent Application, Second Publication, No. Sho 52-44569, Japanese Patent Application, Second Publication, No. Sho 58-19706, and Japanese Patent Application, First Publication, Laid-Open No. Sho 51-79138 and Japanese Patent Application, First Publication, Laid Open No. Sho 58-138758 provide coating materials having a form into which conductive pigment is blended in order to make electro-deposition coating possible.
However, in such coating materials, particulate pigment possessing a relatively large particle diameter, wherein the average particle diameter is 1 micron (.mu.m) or more, such as metallic powders of zinc, metallic carbide powders, or metallic phosphate powders, are employed as the conductive pigment. For this reason, unevenness is produced on the coating film which is formed, or, during press working, flaws resulting from the conductive materials which are added are deposited on the surface of the steel plate, and such unevenness or flaws remain on the surface of the electro-deposited coating, and as a result, even after two or three coats, there is a problem in that such unevennesses or flaws remain on the coating film surface, and there is a disadvantage in that, as a result thereof, it is also impossible to guarantee rust resistance.
Furthermore, in Japanese Patent Application, First Publication, Laid Open No. Sho 58-224174, Japanese Patent Application, First Publication, Laid Open No. Sho 60-197778, Japanese Patent Application, First Publication, Laid Open No. Sho 60-199074, and Japanese Patent Application, First Publication, Laid Open No. Sho 60-174879, inventions relating to organic composite silicate coating films and steel plates coated with such coating films are disclosed. These organic silicate coating films do not contain conductive pigments and are extremely thin coating films having a thickness within a range of 0.2.about.5.0 microns (.mu.m), and possess high corrosion resistance as a result of bonds between an organic binder and colloidal silica, so that such coating films represent a noticeable improvement, particularly in press workabilities.
However, the problem of unevenness in the electro-deposited coating film is present, and in particular, there is a problem in that the coating film thickness of the electro-deposited coating film formed on the organic composite silicate coating film varies greatly in correspondence with the variation in the thickness of the organic composite silicate coating film. That is to say, in places in which the organic composite silicate coating film is thick, the electro-deposited coating film becomes thick, while in place where the coating film is thin, the electro-deposited coating film becomes thin. Accordingly, there is a problem in that as a result of the electro-deposited coating film, those unevennesses are magnified. Additionally, all of these organic composite silicate coating films exhibit a tendency to have poor rust resistance.
Furthermore, the problems described above were solved to a considerable extent by means of methods disclosed in Japanese Patent Application, First Publication, Laid Open No. Sho 62-283161, and Japanese Patent Application, First Publication, Laid Open No. Hei 3-269067; however, these methods possess problems. That is to say, in these methods, the use of a special organic solvent, or the use of special additives, was necessary, and there was a problem in that the adhesion thereof with adhesives such as vinyl chloride sol or the like is poor, and in addition, the electro-deposited coating film lacks a sense of glossiness, that is to say, the coating film is not shiny, and the smoothness thereof is insufficient. In addition, since it is necessary to apply an extremely thin coating film, it is necessary to sufficiently dilute the coating material which is used, and in order to do this, it is necessary to employ a large amount of organic solvent.
In view of the problems and defects present in the conventional technology, the present inventors began research in order to obtain an organic composite-plated steel plate which did not have the problems described above and was novel and possessed great usefulness.
That is to say, the present invention has as an object thereof to provide an organic composite-plated steel plate which is novel and possesses great usefulness, is in a form in which an aqueous resin for organic composite coating which, in particular, has superior adhesion with adhesives, has superior continuous weldabilities, has superior resistance to corrosion after working, and superior electro-deposition coating, and moreover, has superior coating material adhesion and resistance to corrosion, and in particular, the coated surface of which has superior shininess (smoothness) after electro-deposition coating, and furthermore, which has superior rust resistance and the like, and which additionally does not employ large amounts of organic solvent, is pre-coated on a steal material.